Calculation of migration energy using NEB method...
Posted: Thu Jul 26, 2007 12:21 pm
Hi,
I am trying to calculate vacancy migration energy in metallic Fe using NEB method. For this purpose, I followed the method of NEB as outlined in VASP user's guide, i.e. at first I calculated the minimum energy configuration for two end points, then four images were created using linear interpolation method.
These four image configurations are supposed to be in higher energy configurations than the two extremums. But using NEB I am getting exactly opposite result, not only that , all these four images having the same energy.
Whether, NEB method isn't the right tool for doing such type of calculation or is there any mistake in my calculation? Ia m attaching here my INCAR file.
Looking forward for help.
Thanks in advance.
Prithwish
*********
INCAR
*********
System = iron
ISMEAR = 1 ! 1: Methfessel-Paxton order N; -1:Fermi-smearing.
SIGMA = 0.2 ! Smearing factor (in ev)
PREC = High ! sets cutoff and FFT grid
EDIFF = 1E-06 ! energy stoping criterion for electronic iteration
ICHARG = 2 ! start from scratch(this flag determines how to construct the
! initial charge density. 0:calculate charge density from
! initial wave functions; 1:read the charge density from file
! CHGCAR and extrapolate from the old positions to new positions.
! in PAW and LDA+U method be careful (see manual); 2:take
! super-positions of atomic charges; 4: read potential file from
! POT file; +10: non self-consisitent calculation,it means that
!charge density will be kept constant during whole electronic
!minimization.
INIWAV = 1 ! 0:take "jellium wave functions"; 1: fill wave functions arrays
! with random nos (safest full-proof switch).
ISTART = 0 ! start from scratch.Initialize the wave functions according to
! the flag INIWAV
NELM = 100 ! maximum of 100 electronic steps.
NELMIN = 5 ! maximum of two steps.
NELMDL = -5 !no update of charge for 3 steps.
LREAL = Auto !( making the calculation fast)
ALGO = VeryFast ! (making the calculation fast)
NSIM = 4 ! (making the calculation fast);blocked algorithm update;4
! bands
! at a time
ISPIN = 2 ! 1:non-spin polarized calculations; 2:spin-polarized calculation
MAGMOM = 53*1.5 ! (default: NIONS*1;for spin-pol cal a save default:expt
!mag mom *1.2 or 1.5)
SPRING = -5
IMAGES = 4
RWIGS = 1.5
LWAVE = .FALSE.
LCHARG = .FALSE.
LVTOT = .FALSE.
Ionic relaxation
NSW = 400 ! # of steps in optimization (default 0!)
ISIF = 2 ! 0: relax ions, 1,2:relax ions,calc stresses, 3:relax ion+cell
IBRION = 1 ! 1: quasi-NR, 2:CG algorithm for ions
NFREE = 10 ! number of DIIS vectors to save
POTIM = 0.5 ! reduce trial step in optimization
#Parallel Options
LPLANE = .TRUE.
LSCALU = .FALSE.
NPAR = 10 ! how many bands in parallel
NSIM = 4
I am trying to calculate vacancy migration energy in metallic Fe using NEB method. For this purpose, I followed the method of NEB as outlined in VASP user's guide, i.e. at first I calculated the minimum energy configuration for two end points, then four images were created using linear interpolation method.
These four image configurations are supposed to be in higher energy configurations than the two extremums. But using NEB I am getting exactly opposite result, not only that , all these four images having the same energy.
Whether, NEB method isn't the right tool for doing such type of calculation or is there any mistake in my calculation? Ia m attaching here my INCAR file.
Looking forward for help.
Thanks in advance.
Prithwish
*********
INCAR
*********
System = iron
ISMEAR = 1 ! 1: Methfessel-Paxton order N; -1:Fermi-smearing.
SIGMA = 0.2 ! Smearing factor (in ev)
PREC = High ! sets cutoff and FFT grid
EDIFF = 1E-06 ! energy stoping criterion for electronic iteration
ICHARG = 2 ! start from scratch(this flag determines how to construct the
! initial charge density. 0:calculate charge density from
! initial wave functions; 1:read the charge density from file
! CHGCAR and extrapolate from the old positions to new positions.
! in PAW and LDA+U method be careful (see manual); 2:take
! super-positions of atomic charges; 4: read potential file from
! POT file; +10: non self-consisitent calculation,it means that
!charge density will be kept constant during whole electronic
!minimization.
INIWAV = 1 ! 0:take "jellium wave functions"; 1: fill wave functions arrays
! with random nos (safest full-proof switch).
ISTART = 0 ! start from scratch.Initialize the wave functions according to
! the flag INIWAV
NELM = 100 ! maximum of 100 electronic steps.
NELMIN = 5 ! maximum of two steps.
NELMDL = -5 !no update of charge for 3 steps.
LREAL = Auto !( making the calculation fast)
ALGO = VeryFast ! (making the calculation fast)
NSIM = 4 ! (making the calculation fast);blocked algorithm update;4
! bands
! at a time
ISPIN = 2 ! 1:non-spin polarized calculations; 2:spin-polarized calculation
MAGMOM = 53*1.5 ! (default: NIONS*1;for spin-pol cal a save default:expt
!mag mom *1.2 or 1.5)
SPRING = -5
IMAGES = 4
RWIGS = 1.5
LWAVE = .FALSE.
LCHARG = .FALSE.
LVTOT = .FALSE.
Ionic relaxation
NSW = 400 ! # of steps in optimization (default 0!)
ISIF = 2 ! 0: relax ions, 1,2:relax ions,calc stresses, 3:relax ion+cell
IBRION = 1 ! 1: quasi-NR, 2:CG algorithm for ions
NFREE = 10 ! number of DIIS vectors to save
POTIM = 0.5 ! reduce trial step in optimization
#Parallel Options
LPLANE = .TRUE.
LSCALU = .FALSE.
NPAR = 10 ! how many bands in parallel
NSIM = 4